The invention relates to a field replaceable protective cap for an immersion thermocouple tip adapted for repeated use. The use of protective caps in the molten metal, temperature measuring and sample retrieval field is illustrated in U.S. Pat. Nos. 3,791,219 and 3,455,164. The fused quartz or glass thermocouple tubes are fragile and can break during handling and when passing through slag. The samplers shown in those patents, however, are intended for a single use rather than for repeated measurements. U.S. Pat. No. 3,816,183 is illustrative of a refractory fiber sleeve for a repeating use thermocouple.